This invention relates to a corrosion sensing device and more particularly to a corrosion sensor that can be positioned at a desired location in a pipeline system to detect corrosion in the pipeline system.
Pipeline corrosion is generally a hidden problem that often cannot be controlled in many industrial settings. In the chemical industry, corrosion activity can limit equipment life and threaten the reliability of industrial installations. Useful materials in process fluids can cause corrosion of the apparatus used to handle such fluids resulting in a need to curtail operations or shut down a processing system. Correcting the effects of corrosion can thus lead to high maintenance costs. Since it is not often feasible to control corrosion, the effects of corrosion are usually dealt with by removing and replacing the afflicted structure at an estimated stage of corrosion damage.
Thus, one known remedy for dealing with pipeline corrosion is to replace sections of a pipeline at predetermined time intervals rather than risk pipeline rupture and system shutdowns. However, this procedure can be unduly expensive if pipeline is replaced too soon when it still has substantial useful life. Therefore, one of the problems in dealing with pipeline corrosion is accurately determining the optimum time to replace a pipeline.
If information on the extent of corrosion activity is obtainable before significant damage occurs, remedial measures can be taken to repair process equipment before the corrosion activity leads to equipment failure. Thus, an effective corrosion monitoring program typically begins with obtaining information on the extent of corrosion damage or corrosion activity occurring in a particular installation. With regard to pipeline corrosion, a variety of different techniques have been used for determining the amount of corrosion damage or corrosion activity that has occurred in a pipeline used for conveying process fluids.
U.S. Pat. Nos. 4,328,462, 4,768,373 and 5,571,955 disclose the use of probes which are inserted into containers or pipes holding a fluid that causes the pipe or container to corrode. The probes react to the corrosive influence of the fluid in a known correlation to the corrosive response of the material forming the container or pipe. However, the pressures and temperatures often associated with chemical processes severely limit the opportunity to install and remove such probes from the container or pipe, thus limiting access to information on corrosion activity that they are designed to provide.
Other known techniques for determining corrosion activity of process fluids rely on sampling of the process fluids in a processing structure in order to detect corrosive agents or corrosion by-products correlated to corrosion activity. However, sample testing is often time consuming and can thus impose considerable delay between the time of sampling and the reception of analytical results of corrosion tests.
U.S. Pat. No. 4,389,877 describes a system to monitor the amount of erosion taking place within a pipe. Notches are formed in the wall of the pipe to provide an area of reduced strength. A hollow, sealed casing is built around the pipe at the point of reduced strength to provide a leak-tight chamber. A conduit from the hollow, sealed casing is connected to an outside sensing device to monitor pressure changes in the casing. A predetermined pressure change will indicate when a pipe failure occurs at the portion of reduced strength. However, the need to provide areas of reduced strength and a hollow casing around the areas of reduced strength with special sealing material and a sealing collar make it difficult and expensive to employ the '877 system. Moreover, the '877 system allows monitoring only of the pipe area that is notched and sealed with a casing. Thus, areas of the pipeline system which are not easily accessed cannot be monitored. Consequently, remote areas of a pipeline system that might be vulnerable to corrosion failure do not receive adequate monitoring.
It is therefore desirable to provide a reliable method and means for detecting corrosion anywhere in a pipeline system, which means is easily connected to a pipe or sections of pipe and can be used under conditions of high temperature and/or pressure.